- An enclosure which is designed so that none of the processes or ensuing results of its contained components, such as sparking or heating, causes any nearby material to explode.
- An enclosure which hermetically seals the inside from the outside. In this manner, contained components could emit sparks or radiate heat, but these would not be in contact with the surrounding environment.
- An enclosure which is designed to withstand an internal explosion, without provoking any nearby material to explode.
- An enclosure which is able to withstand a nearby explosion and continue functioning within specified parameters.